Horizontal NOR Memory Strings With Segmented Etching Support
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Solution Overview
Problem
Existing methods for forming 3-dimensional NOR-type thin-film memory strings face challenges in achieving structural stability and preventing phenomena like tilting, snaking, or ribboning, especially with taller stacks and narrower active strips, which increases cost-per-bit.
Innovation Solution
The methods involve replacing a single high aspect ratio etch step with two or more etch steps of less challenging aspect ratios, using dielectric pillars for support, and employing multiple masking steps to form wider and more mechanically stable active strips, thereby reducing the risk of structural instability and ribboning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single high aspect ratio etch step is used to form narrow active strips and tall active stacks, then scaling is improved, but structural instability occurs causing tilting, snaking, twisting, bowing, or ribboning
Solution Approach 1:
The patent segments the single high aspect ratio etch step into multiple etch steps with intermediate support structure formation. This divides the challenging single etch into manageable stages, allowing support structures to be introduced at intermediate depths to prevent structural instability during the etching process.
Solution Approach 2:
The patent applies preliminary action by forming support structures (such as mandrels or sacrificial layers) before completing the etch process. These pre-formed supports provide mechanical stability during etching, preventing the active strips from deforming due to their own weight or process stresses.
2Quantity of substance
If taller active stacks with greater number of active layers are formed, then memory capacity is improved, but structural instability is aggravated causing tilting, snaking, twisting, bowing, or ribboning
Solution Approach 1:
The patent segments the formation of tall active stacks into multiple etch stages with intermediate support structure formation. This allows the stack to be built incrementally with stability reinforcement at each stage, preventing cumulative structural degradation that would occur in a single high aspect ratio etch.
Solution Approach 2:
The patent introduces intermediary support structures (mandrels, sacrificial layers, or temporary braces) that act as mediators between the tall active stack and the substrate. These intermediaries provide mechanical support during fabrication, preventing tilting, snaking, and other deformations caused by the height and weight of multi-layer stacks.
3Area of stationary object
If narrower active strips are formed to increase density, then cost-per-bit is reduced, but structural instability increases causing tilting, snaking, twisting, bowing, or ribboning
Solution Approach 1:
The patent segments the narrow active strip formation into multiple controlled etch steps with intermediate support formation. This allows narrow strips to be created with sufficient mechanical support at each stage, preventing the structural failures that would otherwise occur in single-step high aspect ratio etching of narrow features.
Solution Approach 2:
The patent applies preliminary action by forming support structures before and during the narrow active strip etching process. These pre-formed supports compensate for the reduced mechanical strength of narrower strips, preventing deformation while allowing maximum density optimization.
Data Source
AI summary
Various methods overcome the limitations and achieve superior scaling by (i) replacing a single highly challenging high aspect ratio etch step with two or more etch steps of less challenging aspect ratios and which involve wider and more mechanically stable active strips, (ii) using dielectric pillars for support and to maintain structural stability during a high aspect ratio etch step and subsequent processing steps, or (iii) using multiple masking steps to provide two or more etch steps of less challenging aspect ratios and which involve wider and more mechanically stable active strips.